In recent years, according to reconsideration of an energy policy, spreading of supply infrastructure of a hydrogen station for fuel cell automobiles is strongly propelled. In a piping installation where high-pressure fluid flows, such as a hydrogen station, for example, in a case of a pressure of hydrogen, there is a possibility that the pressure reaches high pressure of 80 MPa or more, so that it is necessary to accommodate high-pressure hydrogen gas with a pressure of about 103 MPa (15000 psi) or so in some cases. Therefore, in order to perform on/off of a flow path while maintaining a flow rate of high-pressure fluid, high-pressure trunnion ball valves are frequently used.
In the high-pressure trunnion ball valve, a torque during operation tends to become large because a high fluid pressure is applied to a valve body so that a force acts on a stem shaft mounting portion in a flow path direction from the valve body. Therefore, particularly, in a valve of such a type, it is required to stabilize operability while maintaining valve seat seal performance even under a high pressure and maintaining low torque performance during the operation.
As a ball valve of this type, for example, a high-pressure ball valve of Patent Literature 1 is disclosed. The high-pressure ball valve has stems provided at an upper portion and a lower portion of a ball portion, respectively, and the ball portion is attached inside a body according to a bottom entry structure via these stems. In FIG. 5 and FIG. 6 of the same Literature 1, such a structure is adopted that cylindrical stems are provided on the upper and lower portions of the ball portion to extend integrally, and O-rings are arranged at symmetrical positions regarding a ball of the stems, respectively.
On one hand, a ball valve of Patent Literature 2 is a trunnion ball valve where an upper stem and a lower stem which are cylindrical are integrated in a ball portion, where such a structure is adopted that radial bearings are arranged at symmetrical positions regarding the ball portion of the upper stem and the lower stem of the ball valve and a thrust bearing is arranged on an operation shaft connected to the upper stem.